The invention relates to a multiport switching valve for a liquid flow system.
A valve of the afore-mentioned kind is, for example, known from the US-firm brochure of the company Rheodyne, Catalogue 2000—Injectors, Switching Valves, Fittings, Accessories, page 18.
Such a valve is used in all kinds of liquid handling systems, in particular in chromatography systems. Liquid chromatography is a known method for separating components of trace elements within liquid substrates to be analyzed. For example, in a liquid chromatography (LC)-nuclear magnetic resonance (NMR) system, a chromatography flow coming from a LC separating unit or a peak sampling or trapping unit, is fed to a first decision detector unit and subsequently to a NMR destination detector unit.
For the technique of LC-NMR four automation modes are known, as they are “on-flow”, “stopped-flow”, “time-slicing” and “loop-sampling”.
In a pure on-line coupling, the NMR detector is directly coupled with the liquid chromatograph. In this on-line mode the separated peaks are fed from the LC continuously into the NMR detector to be spectromatically examined on-line therein.
As an alternative to the on-line mode the stopped-flow technique is used, when the flow pump of the LC is stopped as long as a component is investigated inside the NMR detector.
The peak-sampling mode is a mode in which single separated peaks coming from the LC are selected and intermediately stored in a peak-sampling unit for later investigation in the NMR detector.
The time-slicing mode is a clocked mode in which the LC peaks can be investigated in equally timed fractions to observe spectroscopic changes over a certain elusion period.
A LC-NMR system can additionally be hyphenated with a mass spectrometer (MS) leading to just a higher complexity of the system.
A valve of the kind mentioned at the outset is used in the afore-mentioned system in order to switch between the different functions of the system. However, the conventional known valves are restricted in view of their functionality so that usually more than one valve of the conventional design has to be used in order to be able to switch between all the functions of the liquid system. The conventional design of a valve of the kind mentioned at the outset will now be described with reference to FIGS. 9 through 12 of the accompanying drawings.
The conventional valves available on the market, which are designed as rotary valves, are constructed all in a similar way. In FIG. 9, there is shown a valve 10′ configured as an eight-port rotary valve. The valve 10′ comprises a First member 12′ referred to as a stator having a plurality of ports 14′, e.g. eight in the shown example (confer FIG. 10). The ports 14′ are circumferentially distributed in a circular line about the center of the first member 12′ in equal angular intervals. Eight liquid lines 16′ can be connected to the ports 14′, accordingly.
A second member 18′ is connected with the first member 12′ and is movable relative to the first member 12′. The second member 18′ is usually referred to as the rotor. The second member 18′ which is shown in isolation in FIG. 11, comprises a plurality of channels 20′ arranged on the surface of second member 20′ which faces the rear surface of first member 12′. The channels 20′ are, for example, configured as grooves edged in the surface 22′ of second member 18′. The channels 20′ are arranged such that, according to a selected relative position between the first and second member 12′, 18′, one ore more of said channels 20′ connect predetermined ports 14′ of the first member 12′ with one another. One selected relative position is shown in FIG. 12. By rotating the second member 18′ relative to the first member 12′, for example by means of an external driving unit (not shown) via a shaft 26′, another relative position between the first and second member 12′, 18′ can be obtained in order to connect other predetermined ports 14 than as shown in FIG. 12.
Such a design of a valve implies that a number of four or more valves can be necessary for a complex hyphenated LC-NMR system as described above, resulting in a high cost. A further disadvantage is that a large number of valves results in a high dead volume which is detrimental in LC systems where large dead volume affects the accuracy of the analysis.
U.S. Pat. No. 4,923,616 discloses a switching control valve. The known switching control valve comprises a stationary disk as the first member having concentric paths coaxially arranged at suitable intervals about the center of the stationary disk and having downward opening channels, a first group of vertical paths annularly arranged at regular intervals in the circumferential direction with a larger radius than those of the concentric paths and serving as downward opening channels, and a second group of vertical paths annularly arranged at regular intervals in the circumferential direction with a larger radius than that of the circle of the first group and serving as downward opening channels to form a number of counterparts corresponding to the vertical paths of the first group. The valve further comprises as the second member a rotary disk having junction paths comprising first junction paths arranged at suitable positions corresponding to the positions at which the vertical paths of the first and second groups are formed in the stationary disk.
Another multiport switching valve is known from U.S. Pat. No. 3,800,602. That valve comprises an eight port valve block, having a single channel and having a movable valve plate member slidably affixed thereto by a valve plate carrier which in a first position permits simultaneous sampling of a gas stream to be analyzed and back flushing of the chromatograph column and in a second position rapid analysis of the gas sample. By the addition of one or more six port programming valves or equivalent sampling means in series with the eight port valve, the apparatus may function to rapidly analyze two or more separate gas streams.
It is an object of the present invention to provide a multiport switching valve of the kind mentioned at the outset which has an increased functionality so that the number of valves for a complex liquid flow system can be reduced preferably to one valve which can fulfill all requirements of the system.